facile synthesis of intense green-emitting ligdf4:yb,er ... · :yb,er-based upconversion...

Electronic Supplementary Material for Nanoscale

Facile synthesis of intense green-emitting LiGdF4:Yb,Er-based upconversion

bipyramidal nanocrystals and their polymer composites

Hyejin Na,a Jong Seok Jeong,

b Hye Jung Chang,

c Hyun You Kim,

d,e Kyoungja Woo,

a Kipil Lim,

a K. Andre

Mkhoyanb and Ho Seong Jang*

,a,f

aMolecular Recognition Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5,

Seongbuk-gu, Seoul 136-791, Republic of Korea

bDepartment of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington

Avenue SE, Minneapolis, MN 55455, United States.

cAdvanced Analysis Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu,

Seoul 136-791, Republic of Korea

dCenter for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States.

eDepartment of Nanomaterials Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu,

Daejeon 305-764, Republic of Korea

fPresent address:

Center for Materials Architecturing, Korea Institute of Science and Technology, Hwarangno

14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea

*Address correspondence to: [email protected]

Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2014

Figure S1. Photographs of Li(Gd1-xYx)F:Yb,Er UCNP solutions under (a) ambient light and (b) IR

light illumination (980 nm, 2W cw laser). The UCNPs in each solution correspond to the UCNPs

shown in Figure 1 [i: Y = 0 mol%, ii: Y = 20 mol%, iii: Y = 40 mol%, iv: Y = 60 mol%, v: Y = 80

mol%].

Figure S2. Absorption spectrum of LGY0.4F:Yb,Er UCNPs.

Figure S3. UC PL intensity at green and red spectral regions as a function of incident laser power

density. The double-logarithmic plot gives rise to linear plots in which slopes are 1.66 ± 0.04 and 1.94

± 0.03 for green and red emissions, respectively, suggesting that the green and red emissions from

LGY0.4F:Yb,Er UCNPs are dominated by two photon upconversion process.

Upconversion (UC) quantum yield (QY) of LGY0.4F:Yb,Er upconversion tetragonal bipyramids

(UCTBs) was calculated using the QE of β-NaYF4:Yb,Er upconversion nanoparticles (UCNPs)

according to following equation,S1

2

S SRS R

R S R

PL nAbsUCQY UCQY

PL Abs n

(S1)

Where UCQY, PL, Abs, and n indicate the upconversion quantum yield, integrated PL intensity, optical

absorption at excitation wavelength, and refractive index of solvent, respectively, and subscripts S and

R represent sample and reference, respectively. Boyer et al. reported absolute QY of β-NaYF4:Yb,Er

UCNPs under 150 W/cm2, thus the UCQY of the LGY0.4F:Yb,Er UCTBs can be determined by

measuring the UC PL spectra and the absorption values at the excitation wavelength for the

LGY0.4F:Yb,Er and β-NaYF4:Yb,Er UCNPs

According to Boyer et al., absolute UCQE of the β-NaYF4:Yb,Er UCNPs with 30 nm size under ~ 980

nm excitation (power density = 150 W/cm2) is 0.1%.

S2 The 30 nm β-NaYF4:Yb,Er UCNPs were

synthesized by using the synthetic procedure described in the following publications:

Ref. S3, H.-S. Qian and Y. Zhang, Langmuir, 2008, 24, 12123.

Ref. S4, Z. Li and Y. Zhang, Nanotechnol., 2008, 19, 345606.

No changes were made to the reported procedures.

Figure S4. (a, b) TEM and HR-TEM images and (c) XRD pattern of β-NaYF4:Yb,Er UCNPs. The size

of the β-NaYF4:Yb,Er UCNPs is about 30 nm. The spacing between two adjacent lattices are 0.52 nm

which is in good agreement with interplanar d-spacing between {10 0} planes. XRD pattern of the β-

NaYF4:Yb,Er UCNPs is well matched with literature value (JCPDS 28-1192). These results indicate

as-synthesized NaYF4:Yb,Er has single hexagonal phase.

Figure S5. PL spectra of LGY0.4F:Yb,Er and β-NaYF4:Yb,Er under 971 nm excitation with 150 W/cm2

power density. The PL spectra of LGY0.4F:Yb,Er and β-NaYF4:Yb,Er were normalized with the

absorbance value at 971 nm. According to Eq. S1, UCQY of the LGY0.4F:Yb,Er was calculated to be

0.16% which is higher than β-NaYF4:Yb,Er (~ 30 nm) UCNPs.

Figure S6. Intensity ratio of green to red emission of Li(Gd,Y)F4:Yb,Er UCNPs with varying Y3+

concentration from 0 mol% to 80 mol%.

Figure S7. XRD patterns of Li(Gd,Y)F4:Yb,Er UCNPs with varying Y concentrations. When the

concentration of Y was 0 and 20 mol%, tetragonal LiGdF4 phase was not observed. Instead,

orthorhombic GdF3 phase was observed. Thus, in this manuscript, although we describe

Li(Gd,Y)F4:Yb,Er as nominal composition, LiGdF4:Yb,Er and Li(Gd0.6Y0.2)F4:Yb,Er means

GdF3:Yb,Er, and (Gd,Y)F3:Yb,Er, respectively.

Figure S8. HR-TEM images of Li(Gd,Y)F4:Yb,Er UCNPs with varying Y concentration. (a) 0 mol%,

(b) 20 mol%, (c) 40 mol%, (d) 60 mol%, and (e) 80 mol%. Inset of (c) shows FFT diffractogram for

the HR TEM image.

0.36 nm

(101)

0.36 nm

(101)

5 nm 5 nm

(a) (b)

0.36 nm

(101)

Figure S9. TEM image of Li(Gd,Y)F4:Yb,Er rhombic plates with no Y3+

doping.

Table S1. Particle sizes of Li(Gd,Y)F4:Yb,Er with various Y3+

doping concentrations.

Y3+

concentration Crystal structure Particle size

0 mol% Orthorhombic 12.1±1.0 nm × 11.4±1.0 nm,

thickness = 4.0±0.5 nm

20 mol% Orthorhombic 13.4±2.1 nm × 12.3±1.9 nm,

thickness = 4.6±0.3 nm

40 mol% Tetragonal 60.5±1.6 nm × 55.3±1.4 nm



Figure S10. Particle size distribution of Li(Gd,Y)F4:Yb,Er UCNPs with varying Y3+

doping

concentration.

Table S2. Average Bader charge of comprising elements of studied systems.

Li Gd Y F

LiGdF4 1 2.39 n/a -0.85

LiYF4 1 n/a 2.33 -0.83

LiGdYF4 1 2.37 2.33 -0.84

LiGdYF4(101) 1 2.37 2.33 -0.85 (-0.78)a

a Four F

- ions adjacent to Y

3+ dopants are less negatively charged.

Figure S11. STEM images of LGY0.4F:Yb,Er UCTBs (a) without and (b) with short range ordered

arrangement.

Figure S12. (a) Low and (b) high magnification SEM images of LGY0.4F:Yb,Er UCTBs.

Figure S13. (a) HAADF, (b) bright-field HR-STEM images of a single LGY0.4F:Yb,Er UCTB. (c)

colored image of (a). Inset shows Z-contrast variation along line XY. In addition to the overall

variation of Z-contrast across the particle, there are also some peaks in the intensity profile indicating

existence of heavy dopants in the atomic columns

Figure S14. (a) HAADF HR-STEM image of a single LGY0.4F:Yb,Er UCTB and (b) Z-contrast

variation along the line shown in (a). Red arrows indicate low and high intensities for light element (Y)

and heavy element (Yb, Er) doping for Gd sites, respectively.

Figure S15. HAADF HR-STEM images of a single LGY0.4F:Yb,Er UCTB (a) before and (b) after

damage by electron beam. (c) Z-contrast variation along the line shown in (a) and (b). A few STEM

image acquisitions do not change overall intensity variation while overall intensity decreases and the

difference between peak and valley also decreases (~ 90% in this image). After certain threshold, some

regions in the sample start to be damaged quickly as indicated by the arrows in (b).

Figure S16. EELS spectra of (a) Li, (b) F, (c) Gd, (d) Y, (e) Yb, and (f) Er in an LGY0.4F:Yb,Er

UCTBs.

Figure S17. (a) HR-TEM image and (b) XRD pattern of LGY0.45F:Yb,Er UCTBs. Inset indicates FFT

diffractogram which can be indexed to the tetragonal structure of LiGdF4 with the zone axes along the

[010] direction.

Supporting References

S1 G. Chen, T. Y. Ohulchanskyy, A. Kachynski, H. Agren and P. N. Prasad, ACS Nano, 2011, 5,

4981.

S2 J.-C. Boyer and F. C. J. M. van Veggel, Nanoscale, 2010, 2, 1417.

S3 H.-S. Qian and Y. Zhang, Langmuir, 2008, 24, 12123.

S4 Z. Li and Y. Zhang, Nanotechnol., 2008, 19, 345606.

facile synthesis of intense green-emitting ligdf4:yb,er ... · :yb,er-based upconversion...

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